Nan-Loh Yang

Liquid/Liquid interfacial polymerization to grow single crystalline nanoneedles of various conducting polymers.

Single crystalline nanoneedles of polyaniline (PANI) and polypyrrole (PPY) were synthesized using an interfacial polymerization for the first time. The interfacial crystallization of conductive polymers at the liquid/liquid interface allowed PANI and PPY polymers to form single crystalline nanocrystals in a rice-like shape in the dimensions of 63 nm x 12 nm for PANI and 70 nm x 20 nm for PPY. Those crystalline nanoneedles displayed a fast conductance switching in the time scale of milliseconds. An important growth condition necessary to yield highly crystalline conductive polymers was the extended crystallization time at the liquid/liquid interfaces to increase the degree of crystallization. As compared to other interfacial polymerization methods, lower concentrations of monomer and oxidant solutions were employed to further extend the crystallization time. While other interfacial growth of conducting polymers yielded noncrystalline polymer fibers, our interfacial method produced single crystalline nanocrystals of conductive polymers. We recently reported the liquid/liquid interfacial synthesis of conducting PEDOT nanocrystals; however, this liquid/liquid interfacial method needs to be extended to other conductive polymer nanocrystal syntheses in order to demonstrate that our technique could be applied as the general fabrication procedure for the single crystalline conducting polymer growth. In this report, we showed that the liquid/liquid interfacial crystallization could yield PANI nanocrystals and PPY nanocrystals, other important conductive polymers, in addition to PEDOT nanocrystals. The resulting crystalline polymers have a fast conductance switching time between the insulating and conducting states on the order of milliseconds. This technique will be useful to synthesize conducting polymers via oxidative coupling processes in a single crystal state, which is extremely difficult to achieve by other synthetic methods.

Synthesis and Characterization of a Conductive Polyaniline/Clay Hybrid System

This paper presents the synthesis and characterization of polyaniline/montmorillonite hybrid polymer. Montmorillonite is a natural clay mineral. By an intercalative polymerization reaction the hybrid is synthesized. In our study, electron paramagnetic resonance (EPR) spectra were examined together with controls (PANI and clay) with the EPR signals from all the PANI/clay samples showing very high spin density (1019 spins/g polymer). PANI/clay samples show g-values higher than that of pure PANI control. Dc conductivity was measured by a four-point probe method and it was found not to be a linear function of PANI content, but the values are consistent with a percolation threshold.

Three approaches for the synthesis of multiferroic BiFeO 3

Multiferroics represent a class of new materials having potential applications for design and preparation of multifunctional material due to the possibility of the coupling of their coexisting electric and magnetic orderings. The magnetic polarization can be switched by applying an electric field; and the electric polarization, by applying a magnetic field. We report here our attempts using three approaches for fabricating multiferroic ferrites: autoclave, microemulsion and spin-casting. All three methods are based on a precursor solution prepared by dissolving stoichiometric amount of bismuth(III) nitrate and iron(III) nitrate in ethylene glycol. In the autoclave synthesis, sodium hydroxide and hydrogen peroxide were dissolved in DI water with surfactant (Triton x-100, Tx-100) and then the precursor solution was added. The solution was transferred to an autoclave at either 165 or 185 °C for reaction for 24 hours. The two temperatures led to two different bismuth ferrite nanocrystals, Bi2Fe4O9 (165 °C) and BiFeO3 (185 °C). For microemulsion synthesis, sodium hydroxide and hydrogen peroxide were dissolved in DI water and added to an oil solution (cyclohexane and n-butanol) with added surfactant, Tx-100, as “Emulsion I”. “Emulsion II” was made by adding precursor in an oil solution (cyclohexane and n-butanol). “Emulsion I” was allowed to react with “emulsion II” at 80 °C for 3 hours. A non-crystalline bismuth ferrite with a 1:1 atomic ratio for Bi∶ Fe was obtained. The spin-casting method produced the BiFeO3 (BFO) thin film with the desired quality. The quality of the resulting BFO thin film depended strongly on the spinning rates and annealing temperatures. The morphology of all samples was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray dispersive spectroscopy (EDS) was used to confirm the elemental composition in bismuth ferrite samples. X-ray diffraction (XRD) was used for establishing crystalline structures.